1. Field of the Invention
The present invention relates generally to an electrically powered vehicle, such as an electric vehicle (EV), a hybrid electric vehicle (HEV) or a fuel cell vehicle (FCV). More specifically the invention relates to a strategy to diagnose a potential deviation from desired operating characteristics of an electric motor.
2. Background Art
The invention may be used in a hybrid electric vehicle of the type schematically shown in FIG. 1 of co-pending application Ser. No. 09/683,026, filed Nov. 9, 2001, which issued on Feb. 10, 2004 as U.S. Pat. No. 6,688,411; in FIG. 1 of co-pending application Ser. No. 09/712,436, filed Nov. 14, 2000 which issued on Dec. 16, 2003 as U.S. Pat. No. 6,664,657; in co-pending application Ser. No. 10/063,345, filed Apr. 12, 2002, now abandoned; and in co-pending application Ser. No. 09/966,612, filed Oct. 1, 2001, which issued on May 11, 2004 as U.S. Pat. No. 6,735,502. Each of these co-pending applications is assigned to the Assignee of the present invention. The disclosures of these applications are incorporated herein by reference.
The need to reduce fossil fuel consumption and emissions in automobiles and other vehicles predominately powered by internal combustion engines (ICEs) is well known. Vehicles powered by electric motors attempt to address that need. Another alternative solution is to combine a smaller ICE with electric motors into one vehicle. Such vehicles combine the advantages of an ICE vehicle and an electric vehicle and are typically called hybrid electric vehicles (HEVs). See generally, U.S. Pat. No. 5,343,970 to Severinsky.
The HEV may have a variety of configurations. Prior art HEV patents disclose systems in which an operator is required to select between electric motor operation and internal combustion engine operation. In other configurations, the electric motor drives one set of wheels and the ICE drives a different set. These include, for example, a series-hybrid electric vehicle (SHEV) configuration. A series-hybrid electric vehicle has an engine (typically an ICE) connected to an electric motor/generator. The motor/generator, in turn, provides electric power to a battery and a traction motor. In the SHEV, where the traction motor functions as the sole source of wheel torque, there is no direct mechanical connection between the engine and the drive wheels.
A parallel/series hybrid electric vehicle (PSHEV) powertrain has characteristics of both PHEV, described below, and SHEV configurations. It sometimes is referred to as a “split” configuration. In one of several types of PSHEV configurations, the ICE is mechanically coupled to two electric motors in a planetary gear transaxle. A first electric motor, the motor/generator, is connected to a sun gear. The ICE is connected to a planetary carrier. A second electric motor, a traction motor, is connected to a ring (output) gear via additional gearing in a transaxle. Engine torque can power the generator to charge the battery. The generator can also contribute to the necessary wheel (output shaft) torque. The traction motor is used to both contribute wheel torque and to recover braking energy to charge the battery. In this configuration, the generator can selectively provide a reaction torque that may be used to control engine speed. In fact, the engine, motor/generator and traction motor can provide a continuous variable transmission (CVT) effect.
HEV powertrains of this type present an opportunity to better control engine idle speed, compared to conventional vehicles, by using the generator to control the engine.
A parallel hybrid electrical vehicle (PHEV) powertrain configuration has an engine (typically an ICE) and an electric motor that work together in varying degrees to provide the necessary wheel torque to power the vehicle. Additionally, in a PHEV configuration, the motor can be used as a generator to charge the battery from the power produced by the ICE.
Parallel hybrid electric vehicles of known design include an internal combustion engine and an electric motor, typically a high voltage induction motor, which establish parallel power flow paths to vehicle traction wheels. The powertrain has two power sources. The first power source is a combination of an engine and a generator subsystem with a planetary gear set for distributing power through separate power flow paths. The second is an electric drive system comprising a motor, a generator and a battery. The battery acts as an energy storage medium for the generator and the motor. The generator, in a parallel hybrid powertrain, is driven by the engine.
A mechanical power flow path is established between the engine and the transmission torque output shaft. The other power flow path is an electrical power flow path, which distributes power from the engine to the generator, the latter driving the torque output shaft of the transmission through gearing.
When the powertrain is operating with the first power source, engine power is divided between the two paths by controlling the generator speed, which implies that the engine speed can be decoupled from the vehicle speed. That is, the powertrain can act in a manner similar to a continuously variable transmission, where vehicle speed changes do not depend upon engine speed changes. This mode of operation is referred to as a positive split.
The powertrain can act also in a mode of operation that may be referred to as a negative split. In this instance, the planetary gearing will permit the generator to drive the planetary gear set to drive the engine. The combination of the motor, the generator and the planetary gear set thus function as an electromechanical, continuously variable transmission.
When a generator brake is activated, the powertrain will act in the so-called parallel mode in which engine power output is transmitted with a fixed gear ratio solely through a mechanical power flow path in the drivetrain.
When the first power source is active, it can provide only forward propulsion since there is no reverse gear. The engine requires either a generator speed control or a generator brake to transmit engine output power to the drivetrain for forward motion. When the second power source is active, the electric motor draws power from the battery and provides propulsion independently of the engine for driving the vehicle forward and in reverse. The generator, at that time, can draw power from the battery and drive against a reaction brake on the engine output shaft to propel the vehicle forward. This mode of operation is called “generator drive.”
As pointed out above, combining an ICE with an electric motor provides a potential for reducing vehicle fuel consumption and emissions with no appreciable loss of vehicle performance or driveability. The HEV allows the use of smaller engines, regenerative braking, electric boost, and even operation of the vehicle with the engine shut down.
One such area of development for optimizing potential benefits of a hybrid electric vehicle involves calculating torque estimates delivered by an electric motor or motors. An effective and successful HEV design (or any vehicle powertrain propelled by electric motors and optionally capturing regenerative braking energy) requires reliable operation that can be improved through careful diagnosis of electric motor operation. Thus there is a need for a strategy to effectively detect potential discrepancies in electrical operating conditions in an electric motor propelled vehicle's electrical components and sub-systems.
Previous efforts have used rotor position sensors or estimates as part of the control strategy for an electric motor. For example, Jones et al. (U.S. Pat. No. 6,211,633) disclose an apparatus for detecting an operating condition of a machine by synchronizing sampling instants with the machine condition so that reliability data are obtained. The operating condition may be the position of the rotor, in which case estimates of the rotor position and rotor velocity at each of the sampling instants are developed.
Lyons et al. (U.S. Pat. No. 5,864,217) disclose an apparatus and method for estimating rotor position and commutating a switched reluctance motor (SRM), using both a flux/current SRM angle estimator and a toothed wheel generating a magnetic pickup. Phase errors can be compensated by adjusting the angle input to the commutator as a function of estimated speed. Alternately, the flux/current SRM angle estimator can be run in background mode to tune the toothed wheel interrupt angle signal at different speeds.
Drager et al. (U.S. Pat. No. 5,867,004) disclose a control for operating an inverter coupled to a reluctance machine that includes a relative angle estimation circuit for estimating rotor angle for a phase in the reluctance machine.
Lyons et al. (U.S. Pat. No. 5,107,195) disclose a method and apparatus for indirectly determining rotor position in a reluctance motor that is based on a flux/current model of the machine, which model includes multi-phase saturation, leakage, and mutual coupling effects.
Lastly, Acarnley (U.S. Pat. No. 6,005,364) discloses a motor monitoring and control circuit that calculates a value parameter for a position of the motor at given instants. The same parameter (which may be position or speed of a rotor) is then measured at subsequent instants. These values are used to compute a future value of the parameter.
The use of two independent torque estimates to diagnose a potential fault in the electric motor of an electric motor propelled vehicle is unknown in the prior art.